(1) Field of the Invention
The present invention relates to a method for repairing a workpiece, such as a turbine engine component, and more particularly, to a repair method where a desired crystalline structure is initiated from the parent material through an additive layer.
(2) Prior Art
Depositing repair material onto directionally solidified (DS) or single crystal (SC) substrates and fusing this material, i.e. welding, without creating high angle grain boundaries is difficult. This is due to several factors including (1) the inability to control the rate of heating; (2) the inability to control time at temperature; and (3) the inability to control the cooling rate across the entire surface. For example, when the heating source (point source), which is directly influencing the material, is moved across a surface of the substrate being repaired, there is an effect of moving or flowing the heat generated to an area adjacent to the source. As a result of the heat source movement, the area trailing the source begins to cool. It is the control and balancing of the dynamic heating, cooling and time at temperature cycles that have been the focus of development efforts in the past.
In addition to the difficulties associated with the motion of the heat source, starting and stopping of the motion and heat source power have aggravated the thermal cycle. Still further, heat flow difficulties have been additionally complicated by difficulties associated with the variable geometries and thicknesses of the material substrates.
Thus, there is needed a repair technique which effectively eliminates or deals with these difficulties.